This invention relates to a method for recording digital information such as program data necessary for information processing and alphanumerical data to be processed. More particularly, the present invention relates to a method for recording digital information on a recording medium for use in an audio equipment such as an audio cassette tape recorder.
With the widespread use of programmable calculators and personal computers, audio cassette tapes have been widely used as a device for recording programs and data. The reason why the audio cassette tapes are used for recording purposes is that they are one of the cheaper and more easily available recording meduims.
However, a variety of problems come up in recording digital information on a recording meduim designed for audio applications. For example, a recording level adjusting circuit incorporated into a tape recorder or other audio equipment, gives rise to error in reading out digital information. In other words, the conventional audio cassette tape recorder has such a recording level adjusting circuit which manifests a high amplification factor for low sounds and a low amplification factor for loud sound.
The adjusting circuit is of a design suited for recording sound signals (in its broadest aspect) and not for recording digital information. Readout error would be caused especially for the tone burse method as mentioned below.
Ways to record digital information on a recording medium for audio applications can be classified into two categories as follows:
(i) two frequency method PA1 (ii) tone burst method.
The former method (i) is a so-called FM modulation method by which a logic level "1" is represented by f.sub.1 and a logic level "0" by f.sub.2 and recordings are modulated with those different frequencies. The latter method (ii) is a method by which one of logic levels "1" and "0" is modulated with a specific frequency and the other is held at a silent level. In either case, the number of pulses is counted for a given length of time to evaluate the pulse width and the logic level "1" or "0" is determined based upon the number or duration of the pulses.
For those methods silence as well as sound information must be recorded in the record mode where the above discussed recording level adjusting circuit works so that noise is inadvertently recorded on the position on the tape which should never bear any recording. Should the logic level "0" correspond to a non-recorded or silence portion, the logic "0" would be misread as the logic "1."
Furthermore, in the event that a definite signal is recorded immediately after such a silence interval, the leading edge signal level is greatly varied and distorted, thus leading to erroneous level determination.